This invention relates to improved filters and applications therefor.
In many uses of filters, it is important and often imperative that the filter be kept free from liquids, typically water. In addition to having potential adverse impact on the properties of the filter, the penetration of the liquid through a vent filter into the interior space being filtered can have serious adverse impact on the contents of that interior space. For example, nuclear waste containers are often vented by high efficiency particular air (HEPA) filters which vent hydrogen gas, inter alia. Especially useful for such applications are carbon-carbon composite filters, e.g., as described in U.S. Pats. Nos. 4,500,328, 4,772,508, 4,391,873 and 4,152,482 and U.S. Pat. Ser. No. 013,501, filed on Feb. 11, 1987, now allowed. It has recently been observed that when such containers (e.g., drums or plastic bags) are stored unprotected from the weather, water can enter into the interior of the drum or bag through the filter. It appears that when rain accumulates on the top of a container such as a drum, it is sucked into the inside of the drum when the interior temperature goes from relatively hot to relatively cold, thereby creating a slight vacuum. Similar phenomena occur in many other filtering applications. Similarly, there are many applications where a wide variety of filters is inapplicable because of a necessary exposure to water or other liquids. Thus, it is desired to keep liquids away from filter element material, e.g., so that liquid cannot penetrate into interior spaces being filtered and/or out of such interior spaces containing liquids.